Improvements in fluid-pressure operated anti-skid braking systems for vehicles

Description

[0001] This invention relates to improvements in fluid-pressure operated braking systems for vehicles of the kind in which operating fluid from a supply for actuating a wheel brake is supplied to the brake through a skid control unit interposed in a line between the supply and the brake, sensors provided to detect wheel skids and control means responsive to a skid signal produced by any of the sensors are incorporated for determining the existence of a skid and for operating valve means to relieve the pressure of the fluid supplied to the brake at a skid point, and the unit incorporates a memory chamber for storing a memory pressure dependant upon the brake pressure occurring at the skid point to provide a datum or knee point between first and second stages of brake re-application. Such systems will hereinafter be referred to as "of the kind set forth".

[0002] In known fluid pressure-operated braking systems of the kind set forth it is customary for a control unit to be provided for each front wheel of a pair of wheels on opposite sides of a vehicle, known generally in the field of Automobile Engineering as wheels on opposite ends of an axle, so that the behaviour of each front wheel, when the brake is applied, may be controlled independently of the other, according to prevailing road conditions, in order to ensure adequate steerability of the vehicle. In addition it is usual to arrange for a single control unit to control the behaviour of both wheels on the or each remaining axle of the vehicle simultaneously. Specifically a skid signal from one wheel on such an axle will actuate the single control unit to control, simultaneously, the operation of the brakes on both the wheels on that axle.

[0003] In the known constructions described above, the or each control unit incorporates a latch valve which closes at the skid point, thereafter to determine the second stage of brake re-application at which the brake pressure is increased but at a rate of pressure increase less than that at which the pressure increases during the first stage, which is dependant upon the memory pressure.

[0004] When the brakes on the wheels at opposite ends of an axle, other than the steerable wheels, are controlled by independent control units, each responsive to the behaviour of the respective wheel, a problem arises when the vehicle is travelling over a split µ surface with the wheels on opposite sides of the vehicle travelling over surfaces of different co-efficient of friction. Relieving and subsequently modulating the supply of fluid applied to the brake on the wheel travelling over the surface of lower p, and allowing the pressure applied to the brake on the wheel travelling over the surfaces of higher p. to increase at a rate determined by the brake applying means, may act to the detriment of stability of the vehicle.

[0005] An anti-skid braking system is disclosed in GB-A-2 026 113 in which a single valve determines whether a common control chamber is connected to a source of pressure or to a fluid return line. Two brakes on a common axle are connected to the control chamber via respective control valves which determine whether their respective brake is communicated with the control chamber or not. When the system re-applies the brakes following a skid the single valve communicates the control chamber to the source and the control valves are repeatedly operated together to communicate the brakes with the control chamber for successive short intervals so that the pressure in each of the brakes simultaneously moves towards the pressure in the control chamber during the moments when the control valves are open. If the pressure in a first one of the brakes is significantly higher than the pressure in the other, second, brake the pressure difference between the normally higher pressure in the control chamber and the first brake is lower than the corresponding pressure difference between the control chamber and the second brake so that the rate of flow of fluid from the control chamber to the brake is highest for the second brake. Thus the pressure in the second brake gets closer to the pressure in the first brake in steps every time that the two control valves are simultaneously connected to the common control chamber. In the event that at the start of re-application the pressure in the first brake is higher than that in the common control chamber the pressure in the first brake still tends to equalise with the pressure in the control chamber, fluid flowing from the first brake to the second brake through the control chamber.

[0006] According to our invention, in a fluid-pressure operated braking system of the kind set forth, the brakes on the wheels at opposite ends of a common axle are each controlled by a separate skid control unit, and a single latch valve is provided common to both units, the latch valve determining whether the rate of control pressure increase fed to the skid control units is at a relatively higher rate when the latch valve is open before a skid signal is detected or at a lower, restricted, rate when the latch valve is closed when the control means identifies a skid from the first skid point to be sensed by one of the sensors on either wheel, whereafter the rate of re-application of each of the two brakes is controlled independently of the pressure of the other brake and in response to signals from their respective individual sensors, the respective rates of pressure increase in each of the brakes independent first stage of brake re-application being determined by the memory chamber of each respective unit, and in their subsequent respective second stages of brake re-application by a common restricted flow of brake-applying fluid fed to the skid control units.

[0007] When both wheels are travelling over surfaces of identical low µs, both brakes will be released at the same time, and then re-applied in substantially similar sequences, namely in a first relatively rapid stage up to the knee point, determined by the memory pressure, followed by the second, slower, stage by the restricted flow to each brake as aforesaid.

[0008] When a split p. situation arises, both brakes will be released at the same time, but the brake on the wheel which is first to recover is first re-applied through the two stages, followed by re-application of the brake on the other wheel when that wheel has recovered.

[0009] In a preferred construction each skid control unit incorporates a solenoid-operated relay valve, and the latch valve is also operated by a soie- noid, the wheel speed sensors producing signals which are fed into a control module which, in turn, is operative to supply an energising current to all three solenoids in response to a skid signal from one sensor, and thereafter to cause the solenoids of the relay valves to become de-energised to modulate control of the brakes individually, with the current maintained to the latch valve to hold it shut throughout that braking cycle.

[0010] The single control module may supply the energising current to the three solenoid-operated valves on two or more axles of a vehicle.

[0011] One embodiment of our invention is illustrated in the accompanying drawings in which:

Figure 1 is a layout of a two-axle vehicle provided with a relay-operated anti-skid pneumatic braking system;

Figure 2 is a schematic layout in more detail of the system arrangement for one of the two axles;

Figure 3 is a performance graph;

Figure 4 is a end view of one practical form of control unit with all the valves and other components incorporated within a common housing;

Figure 5 is a section on the line 5 - 5 of Figure 4;

Figure 6 is a plan of the unit;

Figure 7 is a section on the line 7 - 7 of Figure 6;

Figure 8 is an end elevation of a one-way valve incorporated in the system and the control unit; and

Figure 9 is a section on the line 9 - 9 of Figure 8.

[0012] In the anti-skid pneumatic braking system illustrated in the drawings brakes 1, 2, 3, 4 are provided on each of two front wheels 5, 6 on a first axle of a vehicle, and on two rear wheels 7, 8 on a second axle of the vehicle, respectively. Each wheel is provided with a respective speed sensor 9, 10, 11 and 12, and the output signals from the sensors are fed into an electronic control module 13 which differentiates the signals and emits energising currents for operating front and rear skid control units 14 and 15.

[0013] Each skid control unit 14, 15 controls the supply of operating pneumatic pressure under the control of a treadle valve 29 to a relay valve 16, 17 for each respective wheel, and each relay valve 16, 17 in turn, controls the supply of air under pressure from a reservoir 18, 19 to the brakes 1 and 2, and 3 and 4.

[0014] Since the arrangements provided on both axles are similar, only that of the rear axle will be described.

[0015] Figure 2 shows, schematically, the construction of the skid control unit 16 for the brakes 3, 4 on the rear axle.

[0016] As illustrated a control pressure from the treadle valve 29 is supplied to an inlet passage 20 and through a normally open latch valve 21, operated by a solenoid 22, to the two relay valves 16 and 17 through passages 23 and 24 respectively. A one-way valve 25, 26 respectively, and a solenoid-operated cut-off valve 27, 28, respectively, each incorporating a normally closed exhaust port, are located in each passage 23 and 24 between the latch valve 21 and the respective relay valve 16, 17.

[0017] Each relay valve 16, 17 is of known construction incorporating a piston 30 working in a bore 31 and operable, in response to the control pressure, to control a main valve 32 between common reservoir 19, the respective brake 3, 4, and a central exhaust passage 39.

[0018] A memory chamber 33, 34 is disposed between each solenoid valve 27, 28 and a connnec- tion in the passage 23, 24 between the one-way valve 25, 26 and the solenoid valve 27, 28, and one-way valves 35, 36 and 37, 38 are provided between the solenoid-operated valves 27, 28 and the chambers 33, 34, and between the memory chambers 33, 34 and the passages 23, 24.

[0019] Finally a one-way valve 40, 41 is provided in a passage 42, 43 leading from the inlet passage 20 to each respective passage 23, 24 on the downstream side of the latch valve 21, between the two one-way valves 25, 37 and 26, 38 respectively.

[0020] Each one-way valve 40, 41 is illustrated on an 15 enlarged scale in Figures 8 and 9 of the drawings. As illustrated each valve comprises a seating 44 of frustoconical outline, and a valve member 45 in the form of a ball for engagement with seating 44. The movement of the ball 45 away from the seating is limited by three angularly spaced inwardly directed radial fingers 46 and, when the ball 45 is in engagement with the seating 44, a limited flow past the ball is permitted through a notch 47 in the seating 44.

[0021] As shown in Figures 4 to 7, all the valves 21, 40, 41, 35, 37, 36, 38, 27, 28, 16 and 17 and other components 33, 34 on each axle are housed and defined within a common housing 51.

[0022] The solenoid 22 of the latch valve and solenoids 47, and 48 of the valve 27 and 28 are adapted to be energised by a current from the control module 13. When such a current is emitted, the solenoid 22 will be energised before, or simultaneously 35 with, the solenoids 47, 48.

[0023] In a normal inoperative position shown in Figure 2 of the drawings, three solenoids 22, 47, and 48 are de-energised so that the latch valve 21 and the valves 47 and 48 are in the open position. Both relay valves 16, 17 are closed to isolate the brakes 3 and 4 from the reservoir 19.

[0024] Upon operation of the treadle valve 29 the control pressure is supplied to the inlet passage 20, and through the open latch valve 21, since the one way valves 40, 41 are closed by that pressure. The control pressure flows through the one-way valves 25 and 26, the passages 23 and 24, and the open valves 27 and 28 to act on the pistons 30 of the relay valves 16, 17. In addition the control pressure enters both memory chambers 33 and 34 through the respective one-way valves 35. The whole system is therefore subjected throughout to an equal control pressure.

[0025] The pressure acting on the pistons 30 causes both relay valves 16, 17 to operate in a known manner to supply air under pressure from the reservoir 19 to the actuators of the brakes in order to apply both brakes 3, 4 simultaneously. The pressure rises with time as shown in the portion A, B of the graph of Figure 3.

[0026] Upon release of the treadle at the end of the braking cycle, air from the brakes 3, 4 is released to atmosphere through the exhaust passages 39, and the control pressure is released through the one-way valves 40 and 41 and an exhaust port on the treadle valve.

[0027] When the brakes 3, 4 are applied as described above and both wheels of the vehicle pass onto a surface of a low co-efficient of friction p. which is sufficiently low for both sensors 11, 12 to emit skid signals substantially simultaneously, an equivalent energising current is emitted by the control module 13 to energise the three solenoids 22, 47 and 48 and thereby close the latch valve 21, and both valves 27 and 28.

[0028] Closure of the latch valve 21 isolates the direct flow of control pressure from the inlet passage 20 to the passages 23, and 24, but a restricted flow into the passages 23 and 24 still takes place through the notches 47 in the seatings 44 of the one-way valve 40, 41.

[0029] Closure of the valves 27, 28 isolates the passages 23 and 24 from the relay valves 16 and 17, which close by the exhaustion to atmosphere through the exhaust port 50 of the control pressures acting on the pistons 30. The pressure then drops from point B as shown in Figure 3.

[0030] Due to the presence of the one-way valve 35, 36, a memory pressure is trapped in each memory chamber, and that pressure is equal to the value of the control pressure applied to the pistons 30 when the skid signals were emitted by the sensors 11, 12 at the skid point.

[0031] When each wheel recovers and the skid signals are cancelled, say when the brake pressure has reduced to point C in Figure 3, indicative that the quality of the road surface has improved sufficiently for the brakes 7, 8 to be re-applied, the control module 13 cuts-off the energising current to the two solenoids 47, 48 so that these two valves open again, but the solenoid 22 remains energised to hold the latch valve 21 in its closed position.

[0032] Opening the valves 27, 28 enables the pressures trapped in the memory chambers 33, 34 to be released through the one-way valves 37, 38 to act on the pistons 30 and act as application pressures to cause the relay valves 16, 17 to operate again to re-apply the brakes 3, 4 as described above.

[0033] Since the volumes of the chambers 33, 34 have to fill the remainder of the passages and the spaces in the bores 31 above the pistons 30, known as the application chambers, such volumes will only be sufficient to raise the brake pressure rapidly in a first stage up to a knee or changeover point D, as shown in Figure 3, which is lower than the said point B. Thereafter the brakes are re-applied, in a second stage, but at a rate of pressure increase slower than that of the first, by the flow to the relay valves 16, 17 of a restricted flow of fluid through the notches 47 in the seatings of the one-way valves 40, 41. This is depicted in the graph of Figure 3 by the line D E.

[0034] Should a further skid condition occur during the application of the brakes in a common cycle, then the sequence of brake release, and brake re-application as described above, will be repeated.

[0035] When the brakes are applied as described above, and one wheel, say the wheel 7, passes onto a surface of low µ with the other wheel travelling over a surface of high µ, a so-called split µ situation arises.

[0036] The sensor 11 emits a skid signal, in response to which the control module 13 energises all three solenoids 22, 47, 48 as described above to close the latch valve 21, and the two valves 27, 28. The pressure applied to the brakes 3, 4 is then relieved as described above.

[0037] Since no skid signal had been emitted by the speed sensor 12, the control module de-energises the solenoid 48 so that the brake 4 can be re-applied substantially instantly, and substantially with no loss of pressure from the memory chamber 34. However any increase in pressure applied to the brake 4 is controlled by a control pressure which can increase only at a rate determined by flow through the notch 47 in the one-way valve 41, due to closure of the latch valve 21. Thus, such a rate of pressure increase is equivalent to that normally experienced in the second stage of brake re-application, as indicated in the graph of Figure 3 by the portion shown in dotted lines from F to G. The point F will normally coincide substantially with the skid point B. However, if there is any delay before the solenoid 48 of the valve 28 becomes de-energised, then the point F may drop below B. Should this occur, the re-application of the brake 4 may be achieved with an initial pressure increase in a first stage at a rate indicated by the slope C D, determined by the necessity for the volume of air trapped in the memory chamber first to make up any volume lost from the passages 24 and the application chamber above the piston 30 of the relay valve 17.

[0038] Controlling application of the brake on a wheel not subjected to a skid condition by means of a control pressure which can increase substantially at the rate of the second stage does not act detrimentally to the stability of the vehicle as might occur if no control is exercised over increase in pressure to the brake on that wheel.

[0039] In practice the control module 13 will take into account the behaviour of all the wheels, and a latch valve 21 on each axle, when closed during a skid cycle, will remain closed until the control module 13 has demanded, from information from all four speed sensors 9, 10 11 and 12, that the vehicle has moved onto a sufficiently good surface for the anti-lock system to be de-activated, and for the latch valves 21 to re-open.

[0040] Naturally the release of the brakes at the end of a braking cycle will de-activate the anti-lock system.

[0041] The one-way valves 25, 26 are provided to ensure that the two brake circuits on each axle are separate from each other, and there can be no mixing of the air on the two circuits, particularly after the latch valve 21 has closed.

Claims

1. A fluid-pressure operated braking system for vehicles in which operating fluid from a supply for actuating a wheel brake (1, 2, 3, 4) is supplied to the brake through a skid control unit (14, 15) interposed in a line between the supply and the brake, sensors (9, 10, 11, 12) provided to detect wheel skids and control means (13) responsive to a skid signal produced by any of the sensors are incorporated for determining the existence of a skid and for operating valve means (27, 28) to relieve the pressure of the fluid supplied to the brake at a skid point, and the unit incorporates a memory chamber (33, 34) for storing a memory pressure dependant upon the brake pressure occurring at the skid point to provide a datum or knee point (D) between first and second stages of brake re-application, characterised in that the brakes (3, 4) on the wheels at opposite ends of a common axle are each controlled by a separate skid control unit, and a single latch valve (21) is provided common to both units, the latch valve (21) determining whether the rate of control pressure increase fed to the skid control units (16, 17) is at a relatively higher rate when the latch valve is open before a skid signal is detected or at a lower, restricted, rate when the latch valve is closed when the control means (13) identifies a skid from the first skid point to be sensed by one of the sensors (11, 12) on either wheel, whereafter the rate of re-application of each of the two brakes (3, 4) is controlled independently of the pressure of the other brake (3, 4) and in response to signals from their respective individual sensors, the respective rates of pressure increase in each of the brakes independent first stage of brake re-application being determined by the memory chamber (33, 34) of each respective unit, and in their subsequent respective second stages of brake re-application by a common restricted flow of brake-applying fluid fed to the skid control units (16,17).

2. A system according to claim 1, characterised in that isolating valve means (25, 26) are interposed in the line between the latch valve (21) and the respective skid control units (16, 17) so as to prevent fluid communication between the skid control units (16, 17) to ensure that the control pressure at one skid control unit (16, 17) does not influence the control pressure at the other skid control unit (16, 17).

3. A system according to claim 1 or claim 2, characterised in that pressure release valve means (40, 41) are provided communicating with the memory chambers (33, 34), the pressure release valve means (40, 41) serving to relieve the control pressure in the memory chambers (33, 34) at the end of a braking operation in which no skid signal is detected, and in which the pressure release valve means (40, 41) also have the dual purpose of providing the restricted flow of control fluid past the latch valve (21) when the brakes are re-applied following a skid.

4. A system according to claim 3, characterised in that the pressure release valve means (40, 41) have a relatively large flow cross-section for flow of control fluid in a first direction to relieve the control pressure in the memory chambers (33, 34), and a smaller flow cross-section effective for said restricted flow of control fluid in the opposite direction to re-apply the brakes.

5. A system according to any preceding claim, characterised in that when both wheels (7, 8) of the axle are travelling over surfaces of the same co-efficient of friction and a skid is identified by the control means (13) both brakes (7, 8) are released and then re-applied together in the first stage of brake re-application at a relatively rapid rate of brake re-application up to the knee point (D) and then further applied in the second stage of brake re-application at a relatively slower rate determined by the separate restricted flow of brake-applying fluid to each brake.

6. A system according to claim 5, characterised in that when one wheel (7, 8) is travelling over a surface of different co-efficient of friction than that of the surface over which the other wheel is travelling and a skid is identified by the control means (13) from a skid signal from any wheel both brakes (3, 4) will be released at the same time, and the brake on the wheel which recovers first is first re-applied through the two stages and the brake on the other wheel is independently re-applied through the two stages when that wheel has recovered.

7. A system according to claim 6, characterised in that when a skid is identified by the control means (13) from a skid signal from only one wheel both brakes are simultaneously released and the brake on the other wheel is immediately re-applied in the first stage of brake re-application with the brake pressure due to the presence of the memory chamber being substantially equal to that which it was immediately before the brakes were released and the other brake thereafter being re-applied in the second stage of brake application, the brake on the one wheel being re-applied through the two stages when that wheel has recovered.

8. A system according to any preceding claim, characterised in that each skid control unit incorporates a solenoid-operated cut-off valve (27, 28), the wheel speed sensors (11, 12) producing signals which are fed into a control module (13) which, in turn, is operative to supply an energising current to all three solenoids (21, 27, 28) in response to a skid signal from one sensor, and thereafter to cause the solenoids of the relay valves to become de-energised to modulate control of the brakes individually, with the current maintained to the latch valve to hold it shut throughout that braking cycle.

9. A system according to any preceding claim, characterised in that during the first stage of brake re-application the brake pressure is increased at a rate dependant on the memory pressure and during the second stage of brake re-application the brake pressure is increased at a slower rate than that at which it is increased during the first stage, and means is provided for producing the second stage of brake re-application, said means comprising a restricted flow valve (40, 41) adapted to be installed in a by-pass passage (42, 43) between a source of control pressure and the downstream side of a latch valve (21) which is mowable at the skid point, the restricted flow valve (40, 41) comprising a seating (44) , a valve member (45) engageable with the seating to cut-off a substantial portion of flow through the valve in one direction, and a restricted orifice (47) defined between the valve member and the seating to permit a restricted flow through the valve when the valve member is in engagement with the seating.

10. A system according to claim 1, characterised in that during said first stage of brake re-application the brake pressure of the two brakes (3, 4) is increased at respective rates dependant on the memory pressure of their respective memory chambers (33, 34), and during said second stage of brake re-appfication the brake pressure of both brakes is increased at a common slower rate than that at which it is increased during each brakes respective first stage of brake re-application, and means (40, 41, 42, 43) is provided in each skid control unit (16, 17) for producing said second stage of brake re-application, said means comprising a restricted flow valve (40, 41) adapted to be installed in respective and independent by-pass passages (42, 43) between a source of control pressure (29) and the downstream side of the latch valve (21) which determines the skid point, each of the restricted flow valves (40, 41) comprising a seating (44) , a valve member (45) engageable with the seating to cut-off a substantial portion of flow through the valve in one direction, and a restricted orifice (47) defined between the valve member (45) and the seating (44) to permit a restricted flow through the valve when the valve member is in engagement with the seating.

11. A system according to claim 10, characterised in that the brake-applying fluid flows from the source (29) of control pressure through the restricted flow valves (40, 41) in the by-pass passages (42, 43) to the skid control units during the second stage of brake re-application and completely by-passes the single latch valve (21).

12. A system according to claim 10 or claim 11, characterised in that the restricted flow valves (40, 41) have a relatively small flow cross-section to control the flow of the brake-applying fluid in the by-pass passages (42, 43) in a first direction of flow which applies the brakes so as only to allow a restricted flow of brake-applying fluid to the two brakes during the second stage of brake re-application, and the restricted flow valves have a relatively large flow cross-section to control the flow of brake-applying fluid in the by-pass passages in a direction of flow opposite to said first direction of flow so as to allow a substantially larger flow of brake-applying fluid in the opposite direction of flow to said first direction of flow when the brake-applying pressure in the respective brakes is relieved by the source of control pressure during normal braking when a skid point has not been detected.

13. A system according to claim 10, characterised in that the restricted orifice (47) in the restricted flow valve (40, 41) comprises a notch in the seating with which the valve member (45) is engageable, and means (46) is incorporated for limiting movement of the valve member away from the seating.

Ansprüche

1. Fluid-betätigtes Bremssystem für Fahrzeuge bei welchem ein Betätigungsfluid von einer Versorgung zur Betätigung einer Radbremse (1, 2, 3, 4) der Bremse durch eine Blockiersteuereinheit (14, 15) zugeführt wird, welche in einer Linie zwischen der Versorgung und der Bremse zwischengeschaltet ist, wobei Sensoren (9, 10, 11, 12) vorgesehen sind, um eine Blockierung eines Rades zu ermitteln und Steuermittel (13) eingebaut sind, welche auf ein Blockiersignal, welches von einem der Sensoren erzeugt ist, ansprechen, um das Vorliegen einer Blockierung zu bestimmen und um Ventilmittel (27, 28) zu betätigen, um den Druck des zu der Bremse an einem Blockierpunkt zugeführten Fluids abzubauen, wobei die Einheit eine Speicherkammer (33, 34) zur Speicherung eines Speicherdrucks in Abhängigkeit von dem Bremsdruck, welcher an dem Bloclcierpunkt auftritt, umfaßt, um einen vorgegebenen Punkt oder einen Kniepunkt (D) zwischen ersten und zweiten Zuständen der Brems-Wiederanwendung vorzusehen, dadurch gekennzeichnet, daß die Bremsen (3, 4) an den Rädern an entgegengesetzten Enden einer gemeinsamen Achse jeweils mittels einer separaten Blockiersteuereinheit gesteuert sind, und ein einzelnes Rückschlagventil (21) gemeinsam für beide Einheiten vorgesehen ist, wobei das Rückschlagventil (21) bestimmt, ob die Größe des Steuerdruckanstiegs, welcher den Blockiersteuereinheiten, (16, 17) zugeführt wird, eine relativ hohe Größe ist, wenn das Rückschlagventil offen ist, bevor ein Blockiersignal ermittelt wird, oder auf einer geringeren, eingeschränkten Größe, wenn das Rückschlagventil geschlossen ist, wenn die Steuermittel (13) eine Blockierung von dem ersten Blockierpunkt, welcher von einem der Sensoren (11, 12) an einem der Räder zu messen ist, feststellt, woraufhin die Größe der Wiederbetätigung jeder der beiden Bremsen (3, 4) unabhängig von dem Druck der anderen Bremse (3, 4) gesteuert wird, und in Abhängigkeit von Signalen von deren jeweiligen Sensoren, wobei die jeweiligen Größen des Druckanstiegs in jeder der unabhängigen ersten Stufen der Bremsen der Brems-Wiederbetätigung durch die Speicherkammer (33, 34) der jeweiligen Einheit bestimmt wird, und in deren nachfolgender jeweiliger zweiter Stufe der Brems-Wiederbetätigung durch eine gemeinsame eingeschränkte Strömung von Bremsbetätigungsfluids, welches den Blockiersteuereinheiten zugeführt wird.

2. System nach Anspruch 1, dadurch gekennzeichnet, daß lsolierventilmittel (25, 26) in der Linie zwischen dem Rückschlagventil (21) und der jeweiligen Blockiersteuereinheit (16, 17) zwischengeschaltet sind, um eine Fluidverbindung zwischen den Blockiersteuereinheiten (16, 17) zu verhindern, um sicherzustellen, daß der Steuerdruck an einer Blockiersteuereinheit (16, 17) nicht den Steuerdruck an der anderen Blockiersteuereinheit (16,17) beeinflusst.

3. System nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß Druckverminderungsventilmittel (40, 41) vorgesehen sind, welche mit den Speicherkammern (33, 34) verbunden sind, wobei die Druckverminderungsventilmittel (40, 41) dazu dienen, den Steuerdruck in den Speicherkammern (33, 34) am Ende einer Bremsbetätigung abzubauen, bei welcher kein Blockiersignal ermittelt wird, und bei welcher die Druckver- minderungsventilmⁱttel (40, 41) weiterhin den Zweck haben, eine verminderte Strömung von Steuerfluid nach dem Rückschlagventil (21) vorzusehen, wenn die Bremsen nach einer Blockierung wieder betätigt werden.

4. System nach Anspruch 3, dadurch gekennzeichnet, daß die Druckverminderungsventilmittel (40, 41) einen relativ großen Strömungsquerschnitt zur Strömung von Steuerfluids in einer ersten Richtung aufweisen, um den Steuerdruck in den Speicherkammern (33, 34) abzubauen sowie einem kleineren Strömungsquerschnittsbereich, welcher für die eingeschränkte Strömung von Steuerfluid in der entgegengesetzten Richtung wirksam ist, um die Bremsen wieder zu betätigen.

5. System nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß, wenn beide Räder (7, 8) der Achse über eine Oberfläche mit demselben Reibungskoeffizient abrollen und eine Blockierung durch die Steuermittel (13) festgestellt wird, beide Bremsen (7, 8) nachgelassen und darauffolgend gemeinsam wieder betätigt werden, und zwar in der ersten Stufe der Brems-Wiederbetätigung bei einer relativ schnellen Rate von Brems-Wiederbetätigungen bis zu dem Kniepunkt (D) und dann weiterhin in der zweiten Stufe der Brems-Wiederbetätigung mit einer relativ langsameren Rate betätigt werden, welche durch die getrennte, beschränkte Strömung des Bremsbetätigungsfluids zu jeder Bremse bestimmt wird.

6. System nach Anspruch 5, dadurch gekennzeichnet, daß dann, wenn ein Rad (7, 8) über eine Oberfläche mit einem unterschiedlichen Reibungskoeffizienten abrollt, als die Oberfläche, über welche das andere Rad abrollt und eine Blockierung durch die Steuermittel (13) von einem Blockiersignal von einem Rad festgestellt wird, beide Bremsen (3, 4) gleichzeitig freigegeben werden, und die Bremse des Rades, welches zuerst wieder in den vorigen Zustand zurückgekehrt, durch die zwei Stufen zuerst wieder betätigt wird und die Bremse des anderen Rades unabhängig davon durch die zwei Stufen wieder betätigt wird, wenn das Rad wieder in den vorherigen Zustand zurückgekehrt ist.

7. System nach Anspruch 6, dadurch gekennzeichnet, daß dann, wenn eine Blockierung durch die Steuermittel (13) von einem Blockiersignal von nur einem Rad identifiziert wird, beide Bremsen gleichzeitig freigegeben werden und die Bremse an dem anderen Rad sofort in der ersten Stufe der Brems-Wiederbetätigung wiederbetätigt wird, wobei der Bremsdruck wegen des Vorhandenseins der Speicherkammer in wesentlichen gleich zu dem ist, welcher vorgelegen hat, direkt bevor die Bremsen freigegeben wurden und die andere Bremse nachfolgend in der zweiten Stufe der Bremsbetätigung wiederbetätigt wird, wobei die Bremse an dem einen Rad durch die zwei Stufen wiederbetätigt wird, wenn das Rad in den vorherigen Zustand zurückgekehrt ist.

8. System nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß jede Blokkiersteuereinheit ein magnetisch betätigbares Abschaltventil (27, 28) umfaßt, wobei die Raddrehsensoren (11, 12) Signale erzeugen, welche in ein Steuermodul (13) geleitet werden, welches wiederum betätigbar ist, um einen Energieversorgungsstrom zu allen drei Magneten (21, 27, 28) in Abhängigkeit von einem Blockiersignal von einem Sensor zuzuleiten und nachfolgend, um zu bewirken, daß die Magneten der Relayventile von der Energieversorgung getrennt werden, um eine Steuerung der Bremsen unabhängig voneinander durchzuführen, wobei die Stromversorgung zu dem Rückschlagventil aufrechterhalten wird, während dieses Bremsbetätigungszyklus geschlossen zu haften.

9. System nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß in der ersten Stufe der Brems-Wiederbetätigung der Bremsdruck in einer Größe erhöht wird, welche von dem Speicherdruck abhängt, und während der zweiten Stufe der Brems-Wiederbetätigung der Bremsdruck mit einer geringeren Größe erhöht wird, als die Größe, bei welcher er während der ersten Stufe erhöht wird, und daß Mittel vorgesehen sind, um die zweite Stufe der Brems-Wiederbetätigung hervorzurufen, wobei diese Mittel ein Ventil (40, 41) mit verminderter Durchströmung umfassen, welches in einem Bypasskanal (42, 43) zwischen der Versorgung des Steuerdruckes und der stromablegenden Seite des Rückschlagsventils (21) einbaubar ist, welches an dem Blockierpunkt bewegbar ist, wobei das Ventil (40, 41) verminderter Durchströmung ein Sitz (44), ein Ventilelement (45), welches mit dem Sitz in Eingriff bringbar ist, um einen wesentlichen Bereich der Strömung durch das Ventil in eine Richtung abzuschalten, und eine verminderte Ausnehmung (47) umfaßt, welche zwischen dem Ventilelement und dem Sitz vorgesehen ist, um eine verminderte Strömung durch das Ventil zu ermöglichen, wenn das Ventilelement sich in Eingriff mit dem Sitz befindet.

10. System gemäß Anspruch 1, dadurch gekennzeichnet, daß während der ersten Stufe der Brems-Wiederbetätigung der Bremsdruck der beiden Bremsen (3, 4) mit jeweiligen Raten vergrößert wird, welche von dem Speicherdruck der jeweiligen Speicherkammern (33, 34) abhängt, und während der zweiten Stufe der Brems-Wiederbetätigung der Bremsdruck der beiden Bremsen mit einer gemeinsamen geringeren Rate als bei der, bei welcher während der jeweiligen ersten Stufe der Brems-Wiederbetätigung jeder Bremse erhöht wird, und daß Mittel (40, 41, 42, 43) in jeder Blockiersteuereinheit (16, 17) vorgesehen sind, um die zweite Stufe der Brems-Wiederbetätigung hervorzurufen, wobei die Mittel ein Ventil (40, 41) verminderter Durchströmung umfassen, welches geeignet ist, in jeweiligen und unabhängigen Bypasskanälen (42, 43) zwischen einer Versorgung von Steuerdruck (29) und der stromabgelegenen Seite des Rückschlagventils (21), welches den Blockierpunkt bestimmt, einbaubar ist, wobei jedes der Ventile (40, 41) verminderter Durchströmung einen Sitz (44), eine Ventilkammer (45), weiche mit dem Sitz in Eingriff bringbar ist, um einen wesentlichen Bereich der Strömung durch das Ventil in eine Richtung abzusperren, und eine verminderte Öffnung (47) umfaßt, welche zwischen dem Ventilelement (45) und dem Sitz (44) vorgesehen ist, um eine verminderte Strömung durch das Ventil zu ermöglichen, wenn das Ventilelement sich in Eingriff mit dem Sitz befindet.

11. System nach Anspruch 10, dadurch gekennzeichnet, daß das Bremsbetätigungsfluid von der Versorgung (29) von Steuerdruck durch die Ventile (40, 41) verminderter Durchströmung in die Bypasskanäle (42, 43) der Blockiersteuereinheit während der zweiten Stufe der Brems-Wiederbetätigung strömt und das einzige Rückschlagventil (21) vollständig umströmt.

12. System nach Anspruch 10 oder 11, dadurch gekennzeichnet, daß die Ventile (40, 41) verminderter Durchströmung einen relativ geringen Strömungsquerschnitt aufweisen, um die Strömung in dem Bremsbetätigungsfluid in den Bypasskanälen (42, 43) in einer ersten Strömungsrichtung zu steuern, welche die Bremsen betätigt, um nur eine verminderte Strömung von Bremsbetätigungsfluid zu den beiden Bremsen während der zweiten Stufe der Brems-Wiederbetätigung zu erlauben, und wobei die Ventile verminderter Durchströmung einer relativ großen Strömungsquerschnitt aufweisen, um die Strömung des Bremsbetätigungsfluids in den Bypasskanälen in einer Strömungsrichtung entgegengesetzt zu der ersten Strömungsrichtung zu steuern, um eine wesentlich größere Strömung von Bremsbetätigungsfluid in der entgegengesetzten Strömung zu der ersten Strömungsrichtung zu ermöglichen, wenn der Bremsbetätigungsdruck in den jeweiligen Bremsen durch die Versorgung von Steuerdruck während der normalen Bremsbetätigung abgebaut wird, wenn ein Blockierpunkt nicht ermittelt wurde.

13. System nach Anspruch 10, dadurch gekennzeichnet, daß die verminderte Öffnung (47) in dem Ventil (40, 41) verminderter Strömung eine Nut in der Dichtung umfast, mit welcher das Ventilelement (45) in Eingriff bringbar ist, und daß Mittel (46) vorgesehen sind, um die Bewegung des Ventilelementes von der Dichtung weg zu begrenzen.

Revendications

1. Système de freinage commandé par la pression d'un fluide, pour des véhicules, dans lesquels un fluide d'actionnement délivré par une source d'alimentation et servant à actionner un frein de roue (1, 2, 3, 4) est envoyé au frein par l'intermédiaire d'une unité de commande d'anti- patinage (14, 15) insérée dans une canalisation présente entre la source d'alimentation et le frein, des capteurs (9, 10, 11, 12) prévus pour détecter des patinages des roues et des moyens de commande (13) sensibles à un signal de patinage produit par n'importe lequel des capteurs sont incorporés pour déterminer l'existence d'un patinage et pour actionner des moyens à valves (27, 28) permettant de réduire la pression du fluide envoyé au frein au moment d'un patinage, et l'unité comporte une chambre d'accumulation (33, 34) servant à stocker une pression d'accumulation en fonction de la pression de freinage apparaissant au moment du patinage de manière à faire apparaître un point de repère ou un coude (D) entre des première et seconde étapes d'un nouveau serrage du frein, caractérisé en ce que les freins (3, 4) montés sur les roues situées aux extrémités opposées d'un même essieu sont commandés chacun par une unité séparée de commande d'antipatinage, et une seule valve de blocage (21) est prévue en commun pour les deux unités, la valve de blocage (21) déterminant si le taux d'accroissement de la pression de commande envoyée aux unités de commande d'anti- patinage (16, 17) possède une valeur relativement supérieure lorsque la soupape de blocage est ouverte avant qu'un signal de patinage soit détecté, ou une valeur inférieure, limitée, lorsque la soupape d'antipatinage est fermée au moment où les moyens de commande (13) identifient un patinage en provenance du premier point de patinage devant être détecté par l'un des capteurs (11, 12) sur l'une ou l'autre des roues, à la suite de quoi la vitesse du nouveau serrage de chacun des deux freins (3, 4) est commandée d'une manière indépendante de la pression appliquée à l'autre frein (3, 4), et en réponse à des signaux délivrés par leurs capteurs individuels respectifs, les taux d'accroissement de la pression étant déterminés pendant chacune des premières étapes indépendantes du nouveau serrage des freins, par la chambre d'accumulation (33, 34) de chaque unité respective, et, pendant les secondes étapes respectives ultérieures du nouveau serrage des freins, par un écoulement commun limité du fluide de serrage des freins, envoyé aux unités de commande d'antipatinage (16, 17).

2. Système selon la revendication 1, caractérisé en ce que des moyens (25, 26) formant valves de sectionnement sont intercalés dans la canalisation s'étendant entre la valve de blocage (21) et les unités respectives de commande d'antipatina- ge (16, 17) de manière à empêcher une communication du fluide entre ces unités pour garantir que la pression de commande appliquée à l'une des unités de commande d'antipatinage (16, 17) n'influe pas sur la pression de commande appliquée à l'autre unité de commande d'antipatinage (16, 17).

3. Système selon la revendication 1 ou 2, caractérisé en ce qu'il est prévu des moyens (40, 41) formant valves de réduction de la pression, qui sont placés en communication avec les chambres d'accumulation (33, 34), les moyens (40, 41 ) formant valves de réduction de la pression servant à réduire la pression de commande dans les chambres d'accumulation (33, 34) à la fin d'une opération de freinage, lors de laquelle aucun signal de patinage n'est détecté, les moyens (40, 41) formant valves de réduction de la pression assumant également le double rôle de fournir l'écoulement limité du fluide de commande en aval de la valves de blocage (21) lorsque les freins sont à nouveau serrés à la suite d'un patinage.

4. Système selon la revendication 3, caractérisé en ce que les moyens (40, 41) formant valves de réduction de la pression possèdent une section transversale d'écoulement relativement large, permettant l'écoulement du fluide de commande dans une première direction en vue de réduire la pression de commande dans les chambres d'accumulation (33, 34), une section transversale d'écoulement plus petite permettant audit écoulement limité du fluide de commande dans la direction opposée de réaliser un nouveau serrage des freins.

5. Système selon l'une quelconque des revendications précédentes, caractérisé en ce que, lorsque les deux roues (7, 8) de l'essieu se déplacent sur des surfaces possédant le même coefficient de frottement et qu'un patinage est identifié par les moyens de commande (13), les deux freins (7, 8) sont desserrés, puis sont à nouveau serrés simultanément pendant la première étape de ce nouveau serrage des freins, à une vitesse relativement rapide de serrage, jusqu'au niveau du coude (D), puis sont à nouveau serrés, lors de la seconde étape du nouveau serrage des freins, à une vitesse relativement plus faible, déterminée par l'écoulement limité séparé du fluide de serrage des freins, qui est envoyé à chaque frein.

6. Système selon la revendication 5, caractérisé en ce que, lorsqu'une roue (7, 8) se déplace sur une surface possédant un coefficient de frottement qui diffère de celui de la surface sur laquelle circule l'autre roue, et qu'un patinage est identifié par les moyens de commande (4) à partir d'un signal de patinage provenant d'une roue quelconque, les deux freins (3, 4) sont desserrés simultanément, et le frein monté sur la roue, qui retrouve la première son fonctionnement normal, est à nouveau serré en premier, et ce dans les deux étapes de serrage, et le frein monté sur l'autre roue est à nouveau serré, d'une manière indépendante, dans les deux étapes de serrage, lorsque le fonctionnement normal de cette roue s'est rétabli.

7 . Système selon la revendication 6, caractérisé en ce que, lorsqu'un patinage est identifié par les moyens de commande (13) à partir d'un signal de patinage provenant d'une seule roue, les deux freins sont simultanément desserrés et le frein monté sur l'autre roue est immédiatement serré à nouveau lors de la première étape du nouveau serrage des freins, la pression de freinage due à la présence de la chambre d'accumulation étant sensiblement égale à celle qui était présente juste avant que le frein ne soit desserré et l'autre frein étant ensuite à nouveau serré lors de la seconde étape du serrage des freins, le frein monté sur la première roue étant à nouveau serré conformément aux deux étapes de serrage, lorsque le fonctionnement normal de cette roue s'est rétabli.

8. Système selon l'une quelconque des revendications précédentes, caractérisé en ce que chaque unité de commande d'antipatinage comprend une valve de fermeture (27, 28) actionnée par un électroaimant, et que les capteurs (11, 12) de la vitesse des roues délivrent des signaux qui sont envoyés à un module de commande (13) qui, à son tour, agit de manière à envoyer un courant d'excitation à un ensemble de trois électroaimants (21, 27, 28) en réponse à un signal de patinage délivré par un capteur, et à désexciter ensuite les électroaimants des servo-soupapes de manière à moduler individuellement la commande des freins, le courant étant maintenu appliqué à la valve de blocage afin de la maintenir fermée pendant la totalité de ce cycle de freinage.

9. Système selon l'une quelconque des revendications précédentes, caractérisé en ce que, pendant la première étape du nouveau serrage des freins, la pression de freinage est accrue à une vitesse qui dépend de la pression d'accumulation et que, pendant la seconde étape du nouveau serrage des freins, la pression de freinage est accrue à ne vitesse inférieure à la vitesse d'accroissement de la pression pendant la première étape, et qu'il est prévu des moyens pour produire la seconde étape du nouveau serrage des freins, lesdits moyens comprenant une valve de limitation d'écoulement (40, 41) adaptée pour être installée dans un passage de dérivation (42, 43) entre une source de pression de commande et le côté aval de la valve de blo-. cage (21), qui est déplaçable au moment du patinage, la valve de limitation d'écoulement (40, 41) comprenant un siège (44), un élément de valve (45) pouvant s'appliquer contre le siège de manière à interrompre une partie substantielle de l'écoulement traversant la soupape dans une direction, et un orifice limité (47) défini entre l'élément de valve et le siège afin de permettre un écoulement limité à travers la valve lorsque l'élément de valve est appliqué contre le siège.

10. Système selon la revendication 1, caractérisé en ce que, pendant ladite première étape du nouveau serrage des freins, la pression de freinage des deux freins (3, 4) est accrue à des vitesses respectives, qui sont fonction de la pression d'accumulation de leurs chambres respectives d'accumulation (33, 34), et que, pendant ladite seconde étape du nouveau serrage des freins, la pression de freinage des deux freins est accrue à une vitesse commune plus lente que la vitesse d'accroissement de la pression pendant chaque première étape respective du nouveau serrage des freins, et qu'il est prévu, dans chaque unité de commande d'antipatinage (16, 17), des moyens (40, 41, 42, 43) servant à appliquer ladite seconde étape du nouveau serrage des freins, lesdits moyens comprenant une soupape de limitation d'écoulement (40, 41) adaptée pour être installée dans des passages de dérivation respectifs et indépendants (42, 43) entre urie source de la pression de commande (29) et le côté aval de la soupape de blocage (21 ), qui détermine l'instant du patinage, chacune des valves de limitation d'écoulement (40, 41) comprenant un siège (42), un élément de valve (45) pouvant s'appliquer contre le siège de manière à interrompre une partie substantielle de l'écoulement à travers la valve dans une direction, et un orifice limité (47) défini entre l'élément de valve (45) et le siège (44) afin de permettre un écoulement limité à travers la valve lorsque l'élément de valve est appliqué contre le siège.

11. Système selon la revendication 10, caractérisé en ce que le fluide de serrage des freins circule depuis la source (9) de pression de commande en traversant les soupapes de limitation d'écoulement (40, 41) situées dans les passages de dérivation (42, 43), en direction des unités de commande d'antipatinage pendant la seconde étape du nouveau serrage des freins, et contourne complètement la valve unique de blocage (21

12. Système selon la revendication 10 ou 11, caractérisé en ce que les valves de limitation d'écoulement (40, 41) possèdent une section transversale d'écoulement relativement étroite pour la commande de l'écoulement du fluide de serrage des freins dans les passages de dérivation (42, 43) dans une première direction d'écoulement, ce qui provoque le serrage des freins, afin de de manière à permettre uniquement un écoulement limité du fluide de serrage des freins en direction des deux freins pendant la seconde étape du nouveau serrage des freins, et que les valves de limitation d'écoulement possèdent une section transversale d'écoulement relativement grande pour commander l'écoulement du fluide de serrage des freins dans les passages de dérivation dans une direction d'écoulement opposée à ladite première direction d'écoulement afin de permettre un écoulement nettement plus important du fluide de serrage des freins dans la direction d'écoulement opposée à ladite première direction d'écoulement, lorsque la pression de serrage des freins, qui est présente dans les freins respectifs, est réduite par la source de pression de commande pendant un freinage normal, lorsqu'aucun patinage n'a été détecté.

13. Système selon la revendication 10, caractérisé en ce que l'orifice limité (47) situé dans la valve de limitation d'écoulement (40.41) comporte une encoche ménagée dans le siège, contre lequel l'élément de valve (45) peut s'appliquer, et des moyens (46) sont incorporés de manière à limiter la course de déplacement de l'élément de valve s'écartant du siège.

Drawing